[Hematological immune-related adverse events of immune checkpoint inhibitors and their management]

Immune checkpoints suppress inappropriate immune responses to self-molecules or cells. Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) expressed in T cells are representative molecules involved in the immune checkpoint system. The recent advent of immune checkpoint inhibitors (ICIs) has drastically changed cancer immunotherapy because a substantial proportion of patients with advanced cancers have responded to ICIs and some of them have been cured. This benefit is due to T-cell rescue from immune suppression in their tumor microenvironment by blocking cluster of differentiation 80/CTLA-4 and PD-L1/PD-1 interactions. However, blocking these interactions also liberates T cells that are reactive to self-antigens from tolerance, resulting in the occurrence of autoimmune diseases, that is, immune-related adverse events. Although the primary target organs are the lungs, gastrointestinal tract, and endocrine glands, hematopoietic cells are also affected in 0.5-3% of patients, potentially resulting in anemia or thrombocytopenia. Because hematopoietic system homeostasis is critical to maintaining life support, the occurrence of grade 3-4 irAEs in the hematopoietic system is directly life-threatening. Herein, we review the relationship between ICIs and toxicities in patients with cancer and describe the characteristics and management strategies for hematological immune-related adverse events.